Self-leveling hydraulic loader



an 6, 1970 E. a LONG 3A87v968 SELF-LEVELI NG HYDRAULIC LOADER Filed Dec 1, 1967 I5 Sheets-Sheet 1 lNVE/VTOE Jam 9 1970 E. a LONG SELF'LEVELING HYDRAULIC LOADER 3 Sheets-Sheet 3 Filed Dec. 4, 1967 United States Patent US. Cl. 214-764 8 Claims ABSTRACT OF THE DISCLOSURE This application discloses a loader unit mounted on a tractor and including a pivotally mounted lift arm pivotally carrying a bucket and all controlled by a hydraulic circuit that includes a lift cylinder, a bucket cylinder and a slave cylinder that is responsive to movement of the lift arm for controlling the bucket cylinder in a fashion to maintain the bucket substantially level. The hydraulic control circuit incorporates a bucket cylinder having a main piston provided with a hollow single-ended piston rod and havng a floating piston for movement relative to the main piston. The passage defined by the hollow piston rod communicates with a region intermediate of the main and floating piston and the slave cylinder which is controlled by the lift arm creates a hydraulic interlock that holds the floating piston against movement in a direction that would permit rearward dumping of the bucket.

BACKGROUND OF THE INVENTION Hydraulically controlled loaders such as are mounted upon and controlled by a tractor type prime mover are known wherein the loader includes a lift arm that carries a pivotally mounted bucket. A lift cylinder is connected to position the lift arm, a bucket cylinder is connected to position the bucket and a slave cylinder is provided to modify the action of the bucket cylinder in accordance with swinging movement of the lift arm for maintaining a substantially level bucket position. A typical self-leveling arrangement of this type, as shown in Long US. Patent No. 3,220,580, has been used with small capacity loaders, but the arrangement is subject to rearward dumping of the bucket in the event of operator error. Rearward dumping of the bucket is inconvenient in any case, and presents a substantial danger in connection with high capacity loaders.

Accordingly, there is a serious need for a hydraulic interlock to prevent the possibility that the hydraulic control circuit might inadvertently be actuated in a fashion to cause rearward dumping.

SUMMARY OF THE INVENTION The present invention provides a hydraulic control circuit arrangement that accomplishes automatic leveling of the bucket during lifting and that incorporates a hydraulic interlock to prevent rearward dumping of the bucket at the top of the lift.

The bucket cylinder arrangement includes a floating piston and a hollow piston rod carrying a main piston and providing a fluid passage communicating with the region of the cylinder intermediate of the floating and main pistons.

The floating piston is associated with an internal hydraulic transfer path leading to a slave cylinder which is responsive to the lift arm and is held fixed by the lift arm whenever the lift arm is stationary. The slave cylinder presents a hydraulic interlock to hold the floating piston stationary in the bucket cylinder at the top of the lift cycle. Improper operation of the control valve applies hydraulic pressure to the bucket cylinder in a sense to dump the bucket rearwardly, but the stationary floating piston positively blocks this action.

In one embodiment in which a loader employs a reverse acting bucket linkage having the bucket cylinder floating and having the hollow single ended piston rod pivoted to the lift arm, the floating piston is in telescoping relation upon the piston rod and acts to oppose extension of the cylinder for preventing rearward dumping of the bucket.

In another embodiment in which a loader employs a forward acting bucket linkage having the bucket cylinder pivoted to the lift arm and having the hollow single ended piston rod floating, the floating piston is at the closed side of the main piston and acts to oppose retraction of the piston rod for preventing reaward dumping of the bucket.

These and other advantages will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view of a tractor with a loader mechanism mounted on the front end thereof;

FIGURE 2 is a right side elevation of the loader mechanism with parts broken away and the bucket and associated control therefor illustrated in the digging and lifting positions and the hydraulic system shown in diagrammatic form;

FIGURE 3 is a fragmentary view similar to FIGURE 2 showing in solid lines the lift arms and bucket in the fully raised position and in dotted lines the positions of the various components after the bucket has been dumped;

FIGURE 4 is an enlarged fragmentary lengthwise sectional view showing a bucket cylinder in accordance with the present invention;

FIGURES 5 and 6 are schematic diagrams showing the hydraulic control circuit for the holder arrangement of FIGURES l to 4;

FIGURE 7 is a fragmentary right side elevation of a loader employing an alternative bucket cylinder arrangement; and

FIGURE 8 is a schematic diagram showing the hydraulic control circuit for the loader arrangement of FIGURE 7.

Referring first to FIGURE 1, there is shown a tractor 12 on which has been mounted at the front end thereof a loader mechanism indicated by the letter L. The loader mechanism includes a main frame structure 10 that is attached to the tractor 12 by suitable fastening means. The frame 10 serves as the main support member and is generally U-shaped in the plan view in that it extends parallel to the sides of the tractor forward of the operator and includes an inverted U-shaped section across the front thereof. The frame 10 includes uprights or stanchions 14, 14 spaced on opposite sides of the tractor 12, which stanchions are connected to the transversely extending inverted U-shaped support 17 by forwardly extending braces 15, 15'.

The various details of the loader construction can be best seen by referring to FIGURES 2 and 3. The loader structure consists of a pair of lift arms or booms 18, 18' located on opposite sides of the tractor. The lift arms 18, 18' are pivotally connected to stanchions 14, 14, respectively, by pivot shaft 22. Connected to the lower ends of the lift arms 18, 18' by means of pivot pins 24, 24, respectively, is the bucket 26. The lower end of lift arm 18 is located between brackets 42, 44 secured to bucket 26 and the pin 24 extends therethrough. The pin 24 extends through the lower end of lift arm 18' and bucket brackets 42, 44'.

The lift arm 18 is pivoted about pin 22 by the operation of hydraulic cylinder 34 through the extension or retraction of piston rod 32 extending outwardly therefrom. The inner or lower end of cylinder 34 is connected to stanchion 14 by pin 36. The outer end of rod 32 is disposed between and connected to pairs of downwardly extending re-inforcing plates 28 that are secured to an intermediate portion of the lift arm 18. Thus, it can be seen that when fluid pressure is applied to the left-hand end of cylinders 34 (FIGURE 2), the lift arm 18 is moved in a counterclockwise direction about pivot pin 22 to raise the bucket 26. Conversely, when fluid is supplied to the opposite end of cylinders 34, the lift arm 18 is moved in a clockwise direction to lower the bucket 26. While only the cylinder 34 for lift arm 18 is shown herein, a duplicate cylinder is provided for lift arm 18 and is connected to operate in conjunction with the cylinder 34.

The positioning of the bucket relative to pivot pins 24, 24' to move the bucket between the digging, loading, and unloading positions is accomplished by the hydraulically operated bucket positioning mechanism shown in various positions in FIGURES 2 and 3. The hydraulically operated bucket psitioning mechanisms connected to each of the lift arms at their opposite end to the bucket 26 are identical and thus only the one disposed between lift arm 18 and brackets 42, 44 will be described in detail.

The bucket positioning mechanism consists of a link 38 that is secured between the upper portion of the brackets 42, 44 by a pin 40. The opposite end of the link 38 is connected by pin 46 between a pair of levers 48. The levers 48 are in turn connected at their opposite ends to an intermediate portion of the lift arm 18 by pin 50. It can thus be seen that pivotal movement of the lever 48 about pin 50 will pivot bucket 26 in the same direction about the end of lift arm 18. To effectuate movement of the linkage mechanism and through it bucket 26, a fluid cylinder 54 is pinned to an intermediate portion of levers 48 by a pivotal connection 52 which comprises a trunnion type support for the cylinder 54. The cylinder 54 has a single ended piston 55 provided with a hollow piston rod 56 that extends forwardly along lift arm 18 and is pivotally connected at its end thereof to a lug or stop 60 by means of pin 58. Thus, introduction of pressure fluid into one end of the cylinder 54 and corresponding withdrawal of fluid from the other end will result in axial movement of cylinder 54 which will cause pivotal movement of levers 48 and corresponding pivotal movement of bucket 26. It is, of course, understood that the two bucket positioning mechanisms operate simultaneously to bring about the desired result.

For effecting leveling control of the bucket 26, a pair of slave cylinders 96, 96 are provided. Each slave cylinder 96, 96' is identically mounted and connected, but only the cylinder 96 is described in detail, it being noted that corresponding parts for cylinder 96' are identified by corresponding numbers of the prime series. The slave cylinder 96 has one end connected to a lower region of the stanchion 14 by a pivot pin 100. A single ended piston 98 operates in the cylinder 96 and has its piston rod 94 pivotally connected to a corresponding pair of brackets 90 by means of a pin 92. The closed end of the cylinder 96 is connected through a hydraulic line 76 to the closed end of the cylinder 54. The rod end of the cylinder 96 is connected through a hydraulic line 78 to the rod end of the cylinder 54.

The leveling action of the present arrangement is functionally similar to that shown in FIGURE 2 of the Long Patent No. 3,220,580, except that a pair of cylinder 96, 96' now operate to perform the function of the single cylinder 96 of said patent. The cylinder 96' in the present arrangement serves to increase the available hydraulic fluid capacity as required by the increased stroke length and fluid displacement capacity of elongated bucket cylinders 54, 54' used herein. The bucket cylinders 54, 54 are different, as is described hereinafter in relation to bucket cylinder 54 shown in FIGURE 4, and the unique hydraulic circuit shown in FIGURE 5.

It may be seen that when the lift arm 18 is raised, it carries the rod 94 upwardly to displace fluid from the rod rod end of cylinder 96 through line 78 to the rod end of cylinder 54' to effectuate downward or retracting movement of cylinder 54 concurrently 'with the upward swing of the lift arm 18. This internal transfer of hydraulic fluid is accompanied by a corresponding flow of fluid from the closed end of the bucket cylinder 54 to the closed end of the slave cylinder 94. Retraction of the cylinder 54 drives the levers 48 clockwise to cause a corresponding progressive clockwise or forward tilt of the bucket 26 relative to the lift arm. Forward bucket tilting produced by the slave cylinder 96 compensates for the tendency of the arcuate travel path of the lift arm 18 to cause a progressive rearward tilting of the bucket 26. The ultimate result of these opposite actions is to maintain the bucket level as it is being raised by the lift arm 18, thereby enabling the bucket to reach maximum height while the load stays in the bucket without spilling out over the front or the back.

This hydraulic compensating control for leveling the bucket throughout its lift cycle is achieved in both the present arrangement and in that of the Long Patent No. 3,220,580. However, in the arrangement of the Long Patent No. 3,220,580, the hydraulic bucket control is essentially independent of the lift cycle, so that the bucket cylinder could be operated full stroke in either direction when at maximum lift position. In the event of operator error, the bucket could be tilted backward to dump the load on the vehicle. While this condition is not dangerous with small loaders handling loose material such as dirt, sand, and the like, it is objectionable for large capacity loaders handling rocks, debris, or even large quantities of dirt and sand.

In accordance with the present invention, the hydraulic circuit provides the loader with an interlock effective at the top of the lift cycle to prevent rearward tilting of the bucket 26 while permitting forward tilting of the bucket for dumping the load. The interlock is developed through the slave cylinders 96, 96 which are held stationary at the peak of the lift cycle because of mechanical connection to the lift arm. When stationary, the slave cylinders provide a hydraulic lock preventing internal fluid transfer from the rod end of the bucket cylinder 54 to the rod end of the slave cylinder 96. In the particular bucket cylinder arrangement utilized herein, the cylinder 54 is of increased length, the main piston 55 is single-ended and is provided with a hollow piston rod 56, with a floating piston 57 being provided within the cylinder 54 in sealingly slidable relation to the rod 56 and to the inner wall 56W of the cylinder.

As previously indicated, the bucket cylinder 54 has its head end connected to the line 76 and its rod end connected to the line 78, but the hollow piston rod 56 provides an internal extension passage 56E communicating with the hydraulic line 70 leading from the valve 66. The variable-length annular space existing between the main piston 55 and the floating piston 57 communicates with the rod passage 56E through lateral ports 56P in the form of wall openings in the hollow rod.

The control valve 66 is conventional and is shown associated with an oil reservoir or sump 62 for a supply of hydraulic fluid, a pump 64 for pressurizing and transmitting fluid from the reservoir to the valve, and an exhaust line for returning hydraulic fluid to the reservoir. The valve includes a lift control lever 82 and a bucket control lever 68. The lift lever 82 is connected by conduits 84, 86 to the head end and rod end, respectively, of the lift cylinder to effect control of the lift arm 18. The bucket lever 68 is connected by conduits 70, 76 to the bucket control circuit. The bucket control lever 68 is maintained in neutral position when the companion lift control lever 82 is to be actuated for raising or lowering the lift arm. In the neutral position of lever 68, no external flow paths are present as both conduits 70 and 76 are closed at the valve.

The bucket cylinder 54, as shown herein, has a closed end cylinder head 101 provided with a laterally opening port 1011 that receives the conduit 76 and has a port 54P leading from its open end and connecting to the conduit 78. The open end is shown with cylinder head 102 that provides a slide bearing for the piston rod 56, with a seal ring 103 acting between the head 102 and the rod 56. The piston 55 is threadedly secured in sealed relation in the end of the piston rod 56 and includes a sleeve section 558 that is clamped in place between the main piston 55 and the end of the piston rod. Piston rings 104, 105 are shown for sealing engagement with the cylinder 54. The piston rod 56 has an inlet connector stub 56S leading laterally therefrom and establishing communication between the extension passage 56E and the conduit 70. Finally, the floating piston 57 has a seal ring 106 engageable with the piston rod 56 and a pair of seal rings 107 engageable with the wall of the cylinder 54.

It may be noted that there actually are three fluid chambers 108, 109 and 110 defined within cylinder 54. The fluid chamber 108 communicates with the closed end of the slave cylinder 96 and with the valve 66 by means of conduit 76. Fluid chamber 109 communicates with the valve 66 by means of conduit 70 and fluid chamber 110 communicates with the rod end of cylinder 96 by means of conduit 78.

The operation of the hydraulic circuit of FIGURE 5 is now described with reference to FIGURES 2 and 3 where different loader positions are shown and FIG- URE 6 where corresponding bucket cylinder positions are shown in a sequential relationship.

At the beginning of the operating cycle, the loader is in the full line position shown in FIGURE 2 and the slave cylinder 96 and bucket cylinder 54 are in the position designated Lower at the bottom of FIGURE 6. After filling the bucket 26, the manual valve lever 68 is actuated to flow fluid from the pump 64 into conduits 76, 76 and to exhaust fluid through conduit 70, 70, thereby expanding bucket cylinder chamber 108 and collapsing chamber 109. The bucket cylinder is extended and the bucket shifts to its Roll Back position, as illustrated in dotted lines in FIGURE 2. In the extreme Roll Back position, the piston 55 abuts the floating piston 57 which, in turn, abuts the cylinder head sleeve 102. The approximate relationships for the Roll Back position of the slave cylinder 96 and the bucket cylinder 54 are shown in the top sequence view of FIGURE 6.

The valve handle 82 is operated to actuate the lift cylinders 34 and raise the booms 18, 18', with each slave cylinder 96, 96 being extended in accordance with the boom movement. During the lift cycle, the valve handle 68 is in neutral position and the extension travel of the slave cylinder piston rods 94, 94' produces an internal fluid transfer through conduits 78, 78. Thus, fluid flows from the rod end of the slave cylinder 96 to the rod end of the bucket cylinder 54 and effects retraction of the cylinder 54, so that the main piston 55 and the floating piston 57 undergo simultaneous movement relative to cylinder 54 in the Lift view of FIGURE 6. The action of the lift arm in swinging from the FIGURE 2 position to the FIGURE 3 position tends to tilt the bucket rearwardly, whereas the action of the slave cylinder 96 tends to tilt the bucket forwardly, with the resultant eflect being to maintain the bucket substantially level.

It should be noted that for a level bucket position at the peak of the lift cycle, the main piston 55 and floating piston 57 are abutting and are at an intermediate travel position within the bucket cylinder 54. Therefore, the invention includes an arrangement to prevent extension of the bucket cylinder and rearward dumping of the bucket. Thus, if the control handle 68 were actuated incorrectly, that is, in a direction to admit fluid from the pump to conduit 76 and to allow exhaust through conduit 70, the bucket could not tip rearwardly. The slave cylinder is fixed in its extended position because the lift arm 18 holds the piston rod 94 extended, so that fluid cannot be transferred from the rod end of the bucket cylinder 54. Therefore, the floating piston 57 is held spaced from the rod end of the cylinder 54. The floating piston 57, in turn, abuts the main piston 55 and holds it against movement toward the rod end of the cylinder 54.

To dump the bucket, the control handle 68 is actuated in a direction to admit fluid from the pump to conduit 70 and to exhaust fluid through conduit 76. Since the slave cylinder is still held by the lift arm, a hydraulic interlock holds the floating piston 57 stationary, while the incoming fluid in conduit 70 expands the chamber 109 and forces the main piston relatively towards the closed end of the bucket cylinder 54 to retract the bucket cylinder and tilt the bucket forwardly. The hydraulic cylinders 96, 54 then assume the position labeled Dump in FIGURE 6.

The lift arm is lowered following the dump cycle to effect retraction of the piston rod 94 of the slave cylinder 96 and produce an internal fluid transfer wherein fluid moves from the closed end of the slave cylinder to expand the chamber 108 at the closed end of the bucket cylinder 54. The main piston 55 and floating piston 57 move in unison to maintain the same capacity in chamber 109 and cause transfer of fluid from the chamber 110 to the rod end of the slave cylinder. The hydraulic circuit and the loader have now completed a full operating cycle.

The bucket linkage and bucket cylinder for the embodiment of FIGURES 1 to 4 are known as a reverse acting type in that the piston rod 56 is pivoted to the lift arm and the cylinder 54 floats with the linkage. In this form, the floating piston 57 is in telescoping relation to the piston rod 56. An alternative embodiment utilizing a forwardly acting bucket linkage is illustrated in FIG- URE 7 wherein the corresponding loader parts and hydraulic controls are designated by corresponding reference characters in the 100 series.

Thus, in FIGURE 7, the loader includes a lift arm 118 carrying a pivoted bucket 126 actuated by a linkage that includes a link 138 connected between a swing lever 148 and the bucket. In this form, a bucket cylinder 154 is pivoted to the lift arm 118 and carries a single ended hollow piston rod 156 that is pivoted intermediately to the lever 148. The lift cylinder piston rod 132 is shown pivoted to the plate 128 at the center of the lift arm and the piston rod 194 of the slave cylinder 196 is shown connected to the plate 190 at the bottom of the lift arm.

The hydraulic control circuit for the bucket 126 is shown in FIGURE 8 and includes a control valve 166 having a handle 168 to regulate inflow and outflow to a pair of conduits 170, 176. The hollow piston rod 156 is equipped wtih a main piston and a floating piston 157 is located between the main piston 155 and the closed end of the bucket cylinder 154.

The pistons for the slave cylinder 196 and bucket cylinder 154 are represented in FIGURE 8 in the relationship that corresponds to the bucket level position at the peak of lift as shown in FIGURE 7. It may be noted that the pistons 155, 157 are abutting and are at an intermediate region along the cylinder 154. Correspondingly, the slave cylinder is held fixed by the now stationary lift arm. To dump from this position, the control valve 166 is actuated to admit fluid from the pump (not shown) into conduit 170 and to exhaust fluid through conduit 176. Thus, fluid enters through the hollow piston rod 156 and forces the piston 155 towards the rod end of the cylinder 154 to extend the piston rod and tip the bucket forwardly. During this action, the floating piston 157 is held looked as the hydraulic fluid at the closed end of the cylinder 154 is trapped by the slave cylinder which is held fixed by the stationary lift.

Correspondingly, if the valve 166 were actuated incorrectly so that fluid pressure were applied through line 176 and exhaust were established through line 170, the bucket 126 would not tip rearwardly, because the floating piston 157 is again held against retracting movement by the action of the fixed slave cylinder.

The remainder of the sequence of operation of the loader embodiment of FIGURES 7 and 8 parallels the sequence of the loader embodiment of FIGURES 1 to 4.

What is claimed is:

1. In a material handling device that includes frame, a life arm pivotally mounted on said frame for vertical swinging movement, a bucket pivotally mounted on said lift arm for vertical swinging movement, means for swinging the lift arm between load and dump positions, and a hydraulic operating mechanism for said bucket including a hydraulic fluid circuit interconnecting hydraulic positioning means mechanically connected between said lift arm and said bucket and operable to elongate and contract for swinging the bucket relative to the lift arm, hydraulic slave means mechanically connected between said lift arm and said frame to elonagte and contract in accordance with swinging movement of the lift arm, means for hydraulically interconnecting said positioning means and said slave means to produce compensating leveling movement of said bucket during swinging movement of said lift arm, and hydraulic interlock means cooperating with and responsive to said slave means when said lift arm is in dump position for interlocking said positioning means against movement in a direction to prevent rearward swinging movement of said bucket.

2. In a material handling device in accordance with claim 1 wherein said hydraulic positioning means includes a bucket cylinder element and a bucket piston disposed therein and having a bucket piston rod element projecting therefrom, one of said elements having pivotal anchorage to said lift arm and the other of said elements having pivotal driving connection to said bucket.

3. In a material handling device in accordance with claim 2 wherein said hydraulic interlock means comprises a floating piston disposed in sealingly slidable relation in said bucket cylinder element to define an intermediate chamber in conjunction with said bucket piston and wherein said piston rod element has a lengthwise passage communicating between said intermediate chamber and said hydraulic fluid circuit.

4. In a material handling device in accordance with claim 1 and wherein said hydraulic positioning means includes a bucket cylinder element having an open end and a closed end, a main piston disposed in said cylinder and having a single-ended piston rod element projecting therefrom, one of said elements having pivotal anchorage to said lift arm and the other of said elements having pivotal driving connnecion to said bucket wherein said slave means includes a slave cylinder, a slave piston therein to define chambers at opposite ends of said slave cylinder and a slave piston rod connected to said slave piston and wherein said hydraulic interlock means includes a floating piston disposed in sealingly slidable relation in said cylinder and cooperable with said main piston to define within said cylinder a first end chamber between said floating piston and one end of said cylinder, a second end chamber between said main piston and the other end of said main and floating pistons, said piston rod element having a lengthwise passage communicating with said intermediate chamber and wherein said hydraulic fluid circuit includes a hydraulic line connecting said first end chamber of said bucket cylinder to one of the end chambers of said slave cylinder and means for selectively connecting a hydraulic pressure line and a drain line to said piston rod passage and to the other end chamber of said slave cylinder and said second end chamber of said bucket cylinder.

5. In a hydraulic bucket positioning mechanism for a loader, .a bucket cylinder having an open end and a closed end, a main piston disposed in said cylinder and having a single-ended piston rod projecting in sealingly slidable relation through said open end, and a floating piston disposed in sealingly slidable relation in said cylinder and cooperable with said main piston to define within said cylinder a first end chamber between said floating piston and one end of said cylinder, a second end chamber between said main piston and the other end of said cylinder and an intermediate chamber between said main and floating pistons, said cylinder having separate port means for each end chamber, each to communicate with a separate exterior hydraulic line, and said piston rod having a lengthwise passage communicating with said intermediate chamber opening exteriorly to communicate with a separte exterior hydraulic line.

6. In a hydraulic bucket positioning mechanism in accordance with claim 5 and wherein said floating piston is disposed in sealingly slidable telescoped relation upon said piston rod such that a portion of said piston rod adjacent said main piston extends through said intermediate chamber, said portion having port means in permanent communication between said rod passage and said intermediate chamber.

7. In a hydraulic bucket positioning mechanism in accordance with claim 5 and wherein said floating piston is disposed on the side of said piston opposite of said piston rod and said piston rod passage opens through said main piston to communicate permanently with said intermediate chamber.

8. In a hydraulic bucket positioning mechanism in accordance with claim 5, the combination with said bucket cylinder and piston rod of a slave cylinder, a slave piston therein to define chambers at opposite ends of said slave cylinder and a slave piston rod connected to said slave piston, said slave cylinder having a port for one of the end chambers thereof connected to the hydraulic line that communicates with one of the end chambers of said bucket cylinder and a port for the other of the end chambers thereof connected to the hydraulic line that communicates with the other of the end chambers of said bucket cylinder, and means for selectively connecting a hydraulic pressure line and a drain line to the hydraulic line communicating with said piston rod passage and to the hydraulic line communicating with said second end chamber of said bucket cylinder.

References Cited UNITED STATES PATENTS 3,402,840 9/1968 Goth 214764 HUGO 0. SCHULZ, Primary Examiner 

